The ice-free state of the rotor blades may be a prerequisite for safe and economical operation of wind turbines. Severe contamination and, in particular, icing of the rotor blades may impair the performance of the system. They may constitute an immediate risk, for example as a result of chunks of ice falling down. Moreover, they may partly cause severe consequential damage, in particular as a result of imbalances and/or different aerodynamic forces. Rotor blade ice detection systems can be used to detect changes to the rotor blades, with the result that suitable countermeasures can be taken. For example, a rotor blade deicing device can be activated or the wind turbine can be switched off if icing of the rotor blades is detected.
United States patent application publication 2010/0111695 discloses a rotor blade ice detection system which records the optical properties of a rotor blade surface using suitable sensors in order to detect icing or adhering snow.
Other known rotor blade ice detection systems evaluate the dynamic behavior of the rotor blades. Such a rotor blade ice detection system is disclosed by EP 2 565 444 A1. In this known system, acceleration sensors are arranged in the rotor blades and a natural frequency of the rotor blade, as determined on the basis of the acceleration data, is monitored for changes. In order to be able to reliably detect icing in this manner, for example, consideration of numerous influencing factors and complex mathematical evaluations are required.
It is difficult to test the proper operation of such a rotor blade ice detection system. For this purpose, icing of the rotor blade must be simulated, for example by fastening weights to the rotor blade. However, this is very complicated since it can be carried out only on site and cannot be carried out or can be carried out only to a very limited extent during ongoing operation, thus requiring the operation of the wind turbine to be interrupted.